With decreasing feature size and more intricate fabrication techniques for wafer-based integrated circuit chips, wafers and the resulting integrated circuit chips have become increasingly sensitive to extraneous or unwanted material on the wafer/chip surface during and after processing. The presence of these unwanted materials either at intermediate fabrication stages or at the end of manufacture often adversely affects product performance reliability. Thus, lack of adequate control of these unwanted materials can result in a loss of yield (reliable chips) and/or failure of the products in use.
Unwanted materials on the wafer/chip surface can be introduced from the external environment (e.g., dust in the air). More often however, unwanted material is introduced as a result of chip fabrication steps which cause deposition of unwanted material on the wafer surface. For example, chemical-mechanical polishing (CMP) processes are used to planarize wafers and/or to planarize layers deposited on wafers (e.g., polycrystalline silicon, tetraethylorthosilicate (TEOS), Al--Cu alloy, etc.). Frequently, residual material detached from the wafer in the course of CMP processes remains on the wafer surface as debris. CMP polishing particles may also remain on the wafer surface after the CMP process step. Other unwanted materials may be introduced to the wafer surface during the course of other processes routinely used in the manufacture of integrated circuit, e.g. processes such as chemical vapor deposition (CVD), wet etching or dry etching.
The desire to control the amount of unwanted material on the wafer/chip surface during manufacture has led to the development of a variety of wafer cleaning processes. Most cleaning processes involve the use of liquids which contact the wafer surface. In some instances, the liquid-based cleaning processes may be combined with mechanical cleaning processes (e.g., brushing off the wafer surface) or other cleaning processes. One technique of introducing mechanical energy into the cleaning process has been by the use of ultrasonic and megasonic transducers. The use of megasonic transducers has been more advantageous since the megasonic frequencies correspond more closely to the resonant frequencies of most unwanted material particles. The use of megasonic transducers has generally involved directing the megasonic energy into the container holding the wafer and cleaning liquid.
While the use of megasonic energy has resulted in improved cleaning, the wafer may still have particles of unwanted material remaining on the surface after removal from the cleaning environment. Thus, there remains a need for further improved cleaning processes.